This invention is directed to an ungelled, curable thermosetting resin produced from an aminoplast, a hydroxyl-containing carboxylic acid, an alkylenimine, and optionally a polyol. More particularly, this invention is directed to such a thermosetting resin prepared from an alkylated melamine-aldehyde condensate, a hydroxyl-containing carboxylic acid, a low molecular weight diol, and an alkylenimine.
U.S. Pat. Nos. 3,965,058 and 3,502,557 to Yurcheshen et al disclose certain ungelled thermosetting products produced by reacting an amine-aldehyde condensate, such as a melamine-formaldehyde or urea-formaldehyde resin with a polyfunctional material containing both hydroxyl and carboxyl groups. It is disclosed that these reaction products can include other components such as a polyol or an epoxy resin, diols being preferred as are epoxides such as reaction products of epichlorohydrin and Bisphenol-A. The disclosed primary utility for the thermosetting reaction products of U.S. Pat. Nos. 3,965,058 and 3,502,557 is in water-dispersed compositions in which the vehicle comprises such reaction products alone or in combination with other resins which compositions are applied to a substrate by electrodeposition.
U.S. Pat. No. 3,519,627 to Coats is directed to cross-linking agents primarily for anionic electrodeposition compositions. The cross-linking agents are produced by introducing carboxyl groups into amino-triazine/aldehyde condensates by transetherifying an alkoxy-alkyl amino-triazine with a mono- to di-hydroxy aliphatic carboxylic acid in the presence of an acid catalyst or by etherifying an alkylol amino-triazine with a mixture of aliphatic monoalcohol and a mono- or di-hydroxy aliphatic carboxylic acid in the presence of an acid catalyst.
U.S. Pat. No. 4,026,855 to Parekh et al is directed to a coating composition primarily for use in electrodeposition containing (A) an aqueous dispersion of a mixture of an ungelled modified cross-linking agent comprising an aminoplast cross-linking agent modified by reaction with a hydroxyl-group containing carboxylic acid, and (B) a water dispersible non-gelled polymeric material of certain description, and (C) an acid solubilizer.
While the above thermosetting resins are good for certain coatings applications, they are deficient in a number of respects for use in coating formulations containing crosslinking agents based on aminoplast resins.
The present invention is directed to ungelled, thermosetting resins which not only can be used advantageously to replace at least a portion of aminoplast crosslinking agents, particularly melamine-aldehyde type condensates, in coating compositions, but also exhibit outstanding properties which make them exceptionally suitable for use as pigment dispersing resins (sometimes referred to as pigment grinding resins.) The ungelled thermosetting resins of the present invention, for example, can be used directly in place of known melamine-aldehyde crosslinking agents without the reduction of properties that can occur in both the uncured compositions and in cured films prepared therefrom when known acrylic or polyester pigment dispersing resins are employed.
An ungelled, thermosetting resin of the present invention, for example, when employed as a pigment dispersing resin, can function both as a crosslinking agent for other components of a coating composition and as a grinding resin without providing deleterious effects associated with the use of a number of known pigment dispersing resins. In addition, the ungelled, thermosetting resins of the present invention can be used in a wide variety of coatings systems since so many coating compositions depend on an aminoplast, especially a melamine-aldehyde condensate, to effect curing.
Moreover, ungelled, thermosetting resins of the present invention can be employed in coating compositions for providing elastomeric, cured films having an excellent combination of hardness and flexibility.
Especially noteworthy is that ungelled, thermosetting resins of the present invention, when employed as pigment grinding resins, provide outstanding color development and excellent transparency in the grinds even for such hard-to-grind pigments as transparent red iron oxide. Resins of the present invention also tend to provide for excellent flow out of pigmented compositions containing conductive black pigments over various primers.
Finally since ungelled, thermosetting resins of the present invention can be produced at very high solids (as will be defined infra), they can be employed in high-solids coatings applications without disadvantageously decreasing the total solids content of the coating compositions. A resin of the present invention can be employed as the major film-forming component of a thermosetting coating composition, but is especially useful for various purposes as a modifying component of thermosetting compositions.